Safe Transmission Temps

sennister · 05-09-2017, 08:42 AM

So we had our first trip out this past weekend with the 25BH. Things went pretty well. Mainly just a water issue with the campground. They said the bathrooms had water on which they did but the shower rooms didn't so we had to haul water to the fill the fresh water tank as we were going to a wedding.

This camper is quite a bit bigger than our previous and a lot heavier. The trip that we went on meant we encountered more rolling hills than what we normally go to and I kept an eye on the transmission temps. Most of the time it was in the low 190s and it did creep up to 210 briefly. Of course every transmission is a bit different but from what I have read you should really watch things if they are getting above 210 for any length of time which we were just started to touch. It wasn't very hot out either. I think temps at the time were about 74F. So much higher air temps will be expected as we get into summer.

Of course everyone will say get a transmission cooler. Yep, they are standard equipment on the Yukon Denali for our model year as are electric fans. So I already have that covered. However from what I have discovered, it is a shared cooler. I guess half of it is an engine oil cooler and half the transmission cooler. Not sure how it is split but I would imagine that the engine oil isn't helping the transmission temps much. Coolant temps in the 200-210 are normal so assuming oil temps are going to be around that and wouldn't that just drag up the transmission temps a bit?

So my question is if anyone that has a GMC/Chevy with these combined engine/transmission coolers, have you added a second aux cooler for the transmission or maybe just disconnected the transmission side of it and went with a dedicated transmission cooler? If so did it help?

Last time I did a transmission fluid change I went with a synthetic. I plan on doing another one this spring but have been holding off pending a decision on what I want to do with the cooler.

NVGun40 · 05-09-2017, 08:57 AM

Just my two cents. I recommend either a second transmission cooler, or there can be found bigger coolers through a lot of off road outlets.

01tundra · 05-09-2017, 08:57 AM

I've seen trans temps up to 210F on various vehicles, but that's only when pulling a grade.

I've read that the fluid will start breaking down at 220F.

Also need to know where you're measuring temps from, most factory sensors are on the return line between the torque convertor and pan, which are going to give you elevated temps that change rapidly.

The important part is the pan temperature, which most vehicles do not measure unless you put an aftermarket sensor in it.

On my '01 Tundra I welded a threaded bung in the pan and had a sensor and gauge for pan temp. I also could see the factory sensor through my SacnGauge II.

When pulling a grade I'd see the factory sensor reading upwards of 215F while the pan temperature remained at a steady 150-160F

Hazman65 · 05-09-2017, 09:00 AM

Interesting question. I tow with a Jeep Grand Cherokee Diesel and keep a careful watch on all the temps, oil, coolant, and transmission. The Jeep makes it very easy as all can be displayed. I have never seen the numbers on my oil or my trans go much over what they are normally when I am not towing. My coolant is another story. It has never gone into the "red" but has gotten close on some long uphill grades. Trans temp stays in the 190s which the display shows in the normal range. The system on the Jeep is sealed! Can't check it the transmission fluid or ever change it! Doesn't sit well with me but I guess they expect the synthetic fluid to last the life of the vehicle and don't want a pathway for any contamination.

DocBrown · 05-09-2017, 09:09 AM

On older TVs you really had to worry about prolonged temps above 220. That's not really an issue anymore unless you are towing for hours at high temps. GM started using DEX VI in 2006. It's a synthetic blend that can take higher temps and offers overall better lubrication.

A couple of years ago we went to Gatlinberg. Outside temps were in the 90s while we got lost on the bypass around Indy. Trans temps were pushing 120 and as high as 127 for a bit. I finally dawned on me that my truck has a custom grill shell on it. I removed the shell and trans temps were 170-190 after that until I pulled up a grade, then 215 or so, but not for more than 15 minutes or so.

All that said it scared me at the time. I stopped at a small shop west of Gatlinburg and they checked my fluid and said don't worry about it, just enjoy your trip. Temps that high are normal in mountains even without towing. I didn't run at those temps for more than 30 minutes at a time, we pulled off and let it cool until I figured out my grill shell was impeding are flow. They said that's fine.

I had the fluid changed last fall, more than a year after that TN trip. Trans is behaving fine. I've put on more than 20k miles since that trip.

Anyway we really did have a great time on that trip. But I spent far too much time worrying about the transmission.

Make sure to change your fluid every 50k. That's in your manual.

sennister · 05-09-2017, 12:19 PM

Yeah the breakdown at 220 or more is what concerns me. If it is in the mid 70s and I am hitting 210 what is it going to be like on a 90F day?

As for where I was measuring. I don't know where the sensor is but through the DIC (Driver Information Center) I can pull up transmission temp.

When I hit these temps it was near our destination where we had gone down a steep grade then back up the other side. On the way home it wasn't as bad. While temps were about the same outside, The steep grade work was as we were leaving the campground before things really started heating up. As we get closer to home things are pretty flat and I was running about 185F.

I have seen how to install aux coolers when there isn't one but I wasn't sure in this case if there is an option to add a secondary cooler coming off the primary or simply unhook the original cooler, leave it there for oil and do a new one for transmission. Maybe that is a better question for a GM specific forum if no one here has done this.

DocBrown · 05-09-2017, 12:31 PM

General consensus on GM specific forums is to run the cooler in line, not eliminate the factory installed cooler. It should follow the flow so that it's the last place the oil is before going back into the transmission.

I put one on my old '03 Trailblazer when I bought our current trailer as it was close to it's max towing our X20E.

Stacked plate coolers are the best but the most expensive. Tube and fin coolers are the cheapest but not as efficient. I used a tube and fin type on the Trailblazer. But that truck didn't have a DIC so I have no idea what the trans temps actually were.

One thing I mentioned but didn't ask you specifically, do you have any kind of grill overlay accessory or anything that could be impeding the air flow?

sennister · 05-09-2017, 12:47 PM

Quote:

Originally Posted by DocBrown

One thing I mentioned but didn't ask you specifically, do you have any kind of grill overlay accessory or anything that could be impeding the air flow?

I saw you mention that but forgot to comment. The grill is OEM but the Denali has that chrome grill which has a bunch of holes in it. So it is different than a normal Yukon. We were on a road trip one winter to Wisconsin Dells not pulling anything and we saw coolant temps spiking. Even though it was middle of winter and it was actively snowing. I didn't check the trans temp but I am sure it was elevated as well. We ended up calling ON Star, they set up a hotel at a town not far from the closest dealer. Once we got out I saw the issue. The road spray from other vehicles caused the entire grill to ice over. The entire front of the truck was encased in ice. We spent the night and made our way to the Dells the next morning.

Running a second aux cooler in line was my plan and positioning it like you said after the OEM cooler and before the transmission would be the best location. I have a cousin who is a service tech at the local Chevy Dealer so he can help me determine direction of flow if I can't figure it out.

sennister · 05-09-2017, 01:43 PM

Hmm. I am going to have to look at the truck tonight. I did some searching over lunch and it appears that it already has two transmission coolers. I know I saw aux transmission cooler on my RPO codes. I assume when I was searching for transmission cooler for a 2011 Denali and coming up with the combo engine/transmission cooler that it was an integrated unit. It is but there is also a secondary dedicated aux cooler mounted in front of the radiator for just the transmission. I should be able to see if it is there by looking through the grill but like I said the RPO code is there.

KNP - H.D. TRANSMISSION OIL COOLER

If this is the case I can't really add another aux cooler. I could probably remove it and add a bigger one.

DocBrown · 05-09-2017, 02:17 PM

My Trailblazer came with a factory installed aux cooler as does my Sierra.

You should still be able to add one. They are typically mounted in front of the radiator and held on with cable ties that have flat ends. You run the hoses under or around the radiator.

jimp · 05-09-2017, 05:38 PM

Newer trannys run hotter than the older ones, part of the game for obtaining better mpg's. Temps of 210 or 220 are ok for short durations. You can always change the ATF more frequently which won't hurt.

JeremiahM · 05-09-2017, 05:41 PM

Not a GM, but my 06 F250 tops out at about 175 (just for a short burst) at the very top in the mountains , and 150-160 on highway pulling our 13k 339flqs, and that's factory setup, cooled by radiator first, then the factory aux cooler, which is huge on these trucks. My parents (02 F250) truck used to run 210-220 easily topping a mountain, and 190-200 just trying to maintain highway speed. I installed the tru cool max stacked plate cooler in line with the factory setup (radiator, then aux, then the aux I added) and it now runs slightly cooler than my 06 in the same situations, worth a look

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JeremiahM · 05-09-2017, 05:43 PM

Here is the one..
http://www.dieselsite.com/specialord...ioncooler.aspx

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repacs0103 · 05-09-2017, 06:29 PM

Agreed with other posters, if you add another cooler, go with a bar and plate type. They aren't too much more and do an amazing job. I had one on my old Volvo wagon that I pulled a pop up with and trans temp never crested 150. Also have 2 on my Cummins swapped Chevy- a huge one for an intercooler and a decent sized one for ps/hydroboost fluid- much less prone to damage than a tube and fin type as well.

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sennister · 05-10-2017, 04:08 AM

Quote:

Originally Posted by jimp

Newer trannys run hotter than the older ones, part of the game for obtaining better mpg's. Temps of 210 or 220 are ok for short durations. You can always change the ATF more frequently which won't hurt.

That is what I have been doing even with the old camper. I will not do the filter every time but it is pretty easy to change the fluid. I have a hoist so it is pretty quick but also have an oil extraction pump.

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WhiteHawker · 05-10-2017, 04:55 AM

I was experiencing the same concern about 2 years ago and after much review and research, decided to install the biggest aftermarket cooler (40K GVW) I could find! I used the following unit on my 2007 Suburban 4L60 and it was a game changer!!

On the hottest days pulling a 30ft Whitehawk combined total weight of TV and TT at approx. 15K lbs the temp does not go past 185! Prior to the install it would see 210-215 all day on hotter days. I would highly suggest this cooler with the thermal bypass (if you live an area of cold winters). The thermal bypass valve is so you can use this cooler in cold weather and the fluid will bypass the cooler until the transmission comes up to operating temperatures.

Average daily tranny temps now without the TT are about 145-160 degrees depending on the day. There are many folks who talk about needing to maintain a minimum tranny temp, however, this cooler setup for me was a big winner!

https://www.amazon.com/Tru-Cool-LPD4...ct_top?ie=UTF8

01tundra · 05-10-2017, 05:48 AM

I've always ran Tru-Cool flat plate auxiliary transmission coolers on all of my vehicles (inline with the factory cooler that's typically located in the radiator).

Haven't added one to my 2500 since it came from the factory with an auxiliary cooler installed.

Tru-Cool LPD Transmission Oil Coolers. Protect Your Investmentâ€”and Your Warranties. | Tru-Cool

I also had the dealership swap out the Denali grill on my truck for an SLT before I drove it off the lot. Mostly because I prefer the look of the SLT grill, but also because I can't see how the Denali grill would pass near as much air as the SLT, there appears to be a lot more free area on the SLT to me.

sennister · 05-10-2017, 06:01 AM

Quote:

Originally Posted by 01tundra

I've always ran Tru-Cool flat plate auxiliary transmission coolers on all of my vehicles (inline with the factory cooler that's typically located in the radiator).

Haven't added one to my 2500 since it came from the factory with an auxiliary cooler installed.

Tru-Cool LPD Transmission Oil Coolers. Protect Your Investmentâ€”and Your Warranties. | Tru-Cool

I also had the dealership swap out the Denali grill on my truck for an SLT before I drove it off the lot. Mostly because I prefer the look of the SLT grill, but also because I can't see how the Denali grill would pass near as much air as the SLT, there appears to be a lot more free area on the SLT to me.

Yeah I agree that the grill design on the Denali seems pretty restrictive.

That is where I am kind of wondering what to do. I already have the combined engine/transmission cooler and OEM aux cooler. I guess that would make it easier since the lines are already run for me to either swap out the OEM with maybe a bigger aux cooler than the OEM that does a better job. The other option is to run a third cooler. Or for now do I skip it and see how it does. I will lose a little fluid doing it later if it is a problem when it is 90 out but not that big of a deal.

sennister · 05-10-2017, 06:03 AM

Quote:

Originally Posted by WhiteHawker

I was experiencing the same concern about 2 years ago and after much review and research, decided to install the biggest aftermarket cooler (40K GVW) I could find! I used the following unit on my 2007 Suburban 4L60 and it was a game changer!!

On the hottest days pulling a 30ft Whitehawk combined total weight of TV and TT at approx. 15K lbs the temp does not go past 185! Prior to the install it would see 210-215 all day on hotter days. I would highly suggest this cooler with the thermal bypass (if you live an area of cold winters). The thermal bypass valve is so you can use this cooler in cold weather and the fluid will bypass the cooler until the transmission comes up to operating temperatures.

Average daily tranny temps now without the TT are about 145-160 degrees depending on the day. There are many folks who talk about needing to maintain a minimum tranny temp, however, this cooler setup for me was a big winner!

https://www.amazon.com/Tru-Cool-LPD4...ct_top?ie=UTF8

Since we are talking the same generation truck. Did you have the KNP RPO Code so you had an Aux that you removed or was it just adding the new one? Transmission is the same in both applications, I just have the 6.2 vs the 5.3 engine.

EDIT: I just looked at the amazon link. Interesting that it has a thermal bypass. Did you install that on yours? It claims to act like a thermostat where it won't flow through the cooler until temps hit 180F. That would mean that if you are running 145-160 in normal driving it actually isn't doing anything unless you left that off. I would consider leaving it off as it reduces a point of failure. However in the middle of winter when it is -20f out it might be nice to have it automatically shut down.

01tundra · 05-10-2017, 06:09 AM

Quote:

Originally Posted by sennister

Or for now do I skip it and see how it does. I will lose a little fluid doing it later if it is a problem when it is 90 out but not that big of a deal.

Every one I've installed I may have lost a few drops of fluid, just have some ties of some sort to keep the cut hoses elevated while you're hooking them up.

I haven't had to even add fluid to the transmissions, I just fill the cooler through the top port with a hose and bottle pump prior to hooking the final hose up.

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